Elsevier

Acta Oecologica

Volume 31, Issue 2, March–April 2007, Pages 185-192
Acta Oecologica

Original article
Seasonal patterns of activity and community structure in an amphibian assemblage at a pond network with variable hydrology

https://doi.org/10.1016/j.actao.2006.09.006Get rights and content

Abstract

We studied community structure and seasonal activity patterns in a system of four ponds with seasonally-variable hydrology at a Mediterranean area in central Italy. We used a set of field methods to assess species presence and relative frequency of observation. The network of ponds was inhabited by six species of amphibians, two salamanders and four frogs. The breeding phenology of the six species did not vary remarkably among ponds, but there were significant differences among species in use of ponds. Factorial analysis of pond similarity drawn from percentage composition of the amphibian fauna, revealed that each of the four ponds was treatable as independent units, with no influence of relative inter-pond distance. PCA analysis allowed us to spatially arrange the amphibian species into three main groups: two were monospecific groups (i.e., Triturus vulgaris and Bufo bufo) and the third consisted of those species that selected not only the largest-deepest ponds, but also the ephemeral ones (i.e., Triturus carnifex, Hyla intermedia, the green frogs and Rana dalmatina). Our results suggest that the inter-pond differences in riparian vegetation, water depth, aquatic vegetation structure/abundance, and soil composition may produce differences among pond ecological characteristics (i.e., water turbidity and temperature, shelter availability, abundance of oviposition micro-sites), which may in turn influence different patterns of use by amphibians. To our knowledge, this is the first study emphasizing the potential role of heterochrony in the maintenance of a high species richness in Mediterranean amphibian communities. Preservation of freshwater vertebrate biodiversity requires management and protection not only of the main ponds and water bodies but also the temporary and ephemeral shallow ponds.

Introduction

Ideally, since the Lotka-Volterra age, ecologists have thought that sympatric species which are potentially in competition each another tend to partition their niche in order to decrease competition, with the three main niche axes being the temporal, the trophic, and the spatial dimensions (e.g., Pianka, 1986). Thus, differential use of the spatial resource by roughly sympatric species is one of the main niche elements separating species and facilitating their coexistence when the resources are limited (e.g., Ricklefs and Schluter, 1993). This pattern has been well documented in disparate animals living in contrasting environmental conditions, including carnivorous mammals in the rainforest (e.g., Chuang and Lee, 1997, Ray and Sunquist, 2001, Angelici and Luiselli, 2005a), rodents and insectivores in the rainforest (Angelici and Luiselli, 2005b), and lizards in the deserts (e.g., Pianka, 1986). Partitioning of spatial resources of ectothermic terrestrial vertebrates (reptiles and amphibians), has been demonstrated to be a crucial structuring element for the communities of some taxonomic groups such as lizards (e.g., Pianka, 1986, Barbault, 1991) and terrestrial turtles (Luiselli, 2006a), but not for others such as snakes (Mushinsky and Hebrard, 1977a, Mushinsky and Hebrard, 1977b, Luiselli, 2006b). Thus, generality of spatial niche partitioning pattern has been questioned for the evolution of ectothermic communities. In this regard, study of new community systems may prove useful in order to explore eventual generalisations for ectothermic community ecology functioning. Obviously, novel study systems occurring in environmental conditions/habitats/climates that have been poorly studied up to date are especially noteworthy if we want to have a complete look at the evolution and patterns of spatial niche use by ectothermic vertebrates.

Amphibians are well suited for this type of study (e.g., Toft, 1985), but unfortunately there are considerable biases with regards to geographic regions and habitats where amphibian community studies have been conducted. Indeed, there has been considerable effort by ecologists to study the community organization and assembly rules of amphibians in tropical regions (e.g., Inger, 1969, Barbault, 1987, Barbault, 1991, Toft, 1980, Toft, 1981, Parris and McCarthy, 1999, Eterovick and Sazima, 2000, Neckel-Oliveira et al., 2000, Luiselli et al., 2004) or in temperate regions of North America (e.g., Pechmann et al., 1989, Cortwright and Nelson, 1990, Sredl and Collins, 1992, Semlitsch et al., 1996, Jaeger et al., 1998, Brodman et al., 2003), and Europe (e.g., Beebee, 1983, Beebee, 1985, Pavignano et al., 1990, Martínez-Solano et al., 2003, Ravkin et al., 1993). Almost nothing has been investigated with regards to the Mediterranean communities of amphibians (but see Diaz-Paniagua, 1988, Jakob et al., 1998, Jakob et al., 2003). However, these Mediterranean communities may be relatively species-rich, at least compared to temperate communities of amphibians (e.g., Jaeger et al., 1998, Ravkin et al., 1993). Overall, amphibian communities seem to be especially moisture-sensitive, and this is clearly reflected in the great difference in numbers of leaf litter frog species between forests with long dry seasons and those with short ones, compared to the relatively small differences in numbers of lizard species in the same forest floors (Heatwole, 1982). In the great majority of cases, amphibians are generalist arthropophagous (see Duellman and Trueb, 1994, for a review), and hence are likely to partition their spatial niche to coexist (Griffiths and Mylotte, 1987). This has been clearly demonstrated for instance in the Neotropical frog genera Eleutherodactylus (Heatwole, 1982) and Leptodactylus (Heyer and Bellin, 1973). Other authors pointed out the importance of annual/daily activity patterns associated to spatial aspects of niche separation of sympatric amphibian species (Dankers, 1977, Semlitsch and Pechmann, 1985, Morin, 1987, Morin et al., 1990, Lawler and Morin, 1993, Semlitsch et al., 1993, Jakob et al., 2003). The temporal aspect of the niche should also be accurately considered in long-term community studies relating to amphibians (Semlitsch et al., 1996). The structure and composition of amphibian communities tend to change considerably across years due to historical changes in habitat modifications (Lea et al., 2005).

Furthermore, most of the aquatic-breeding amphibians from temperate and Mediterranean regions are characterized by cyclic (generally annual) reproductive patterns and aggregation at ponds for a very short period when they may reach high densities. In such climatic conditions, reproductive activity patterns respond to temperature, rainfall and water availability (Pechmann et al., 1989, Jakob et al., 2003, Della Rocca et al., 2005).

Because of the issues mentioned above, the study of spatio-temporal aspects of niche use by a species-rich Mediterranean amphibian community may be useful to understand how community-specific composition is structured, responding to the need of exploiting limited resource, at least if the analysis is done at a very small spatial scale, revealing the evidence of microhabitat partitioning.

Here, we examine the spatial and temporal aspects of a Mediterranean community of amphibians at a very small spatial scale; i.e., at the level of four small ponds interspersed into an agro-natural landscape. We aim at answering to the following key questions: 1) do the various species respond in a species-specific way to the available conditions? 2) If yes, does it depend on ecological constraints at the proximate environmental level or on community assembly (=synecological) reasons? 3) Is there any effect of pond vicinity on the observed patterns? 4) What are the conservation implications of our study?

Section snippets

Study area

The field work was carried out at Canale Monterano (190 m a.s.l.; N46.8107°, E6.7181°) in the Regional Natural Reserve of Monterano (Province of Rome, Italy). Samples were taken over an area of five hectares within a tuff quarry abandoned for about 30 years. The peculiar permeability properties of tuffaceous substrate allowed the formation of some lentic aquatic habitats fed predominantly by rainfall. In terms of water permanence, two main aquatic systems were detected: one permanent and one

Results

The six amphibian species showed different patterns of occupancy and activity in their use of the four ponds (Table 1). Newt species reached the ponds in Autumn, breeding and feeding continuously while in water until May, when they returned to land. Triturus carnifex used ponds P3 and P4 for reproduction and feeding, but only subadults were observed sporadically in the ponds P1 and P2. Triturus vulgaris used all the ponds for both reproduction and trophic activities. Bufo bufo was observed

Discussion

Compared with most of the previous studies on the ecology of temperate amphibian communities, our own is one of the first in Europe analysing the spatial assemblage structuring at the pond level rather than at the landscape level (e.g., see Diaz-Paniagua, 1990, Neckel-Oliveira et al., 2000; Brodman et al., 2003). We analysed not only community composition but also annual phenology and type of activity exhibited by the various species at adult stage in the four ponds, linking the

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